1. Field of the Invention
The present invention relates generally to an apparatus and method for inserting a coating device into the passageway of a live gas pipeline and propelling said coating device bi-directionally through said live gas pipeline passageway. Particularly, this invention relates to an entry unit coupled with a propulsion apparatus for inserting a coating device into live gas pipeline and precisely propelling the coating device laterally through long lengths of the live gas pipeline.
2. Description of the Related Art
A dilemma has arisen in the gas and gas transportation industry. Low-moisture gas, such as propane or natural gas, has replaced high-moisture manufactured gas, such as coal gas, as a source of domestic and industrial fuel. Traditionally and for many decades coal or other high-moisture gases were fed to customers by underground pipes. Typically these gas pipelines were constructed of individual lengths of pig or cast iron pipe. These individual lengths of pipe were commonly joined together by bell or lap joints that were sealed with a combination of a filler material and lead. Several different types of filler material were used including horsehair, yarn, jute and hemp. It was discovered that, as many municipalities converted from high-moisture manufactured gas to the relatively low-moisture propane or natural gas, the filler material in the pipe joints would dry out. As these filler materials dried out they would decompose and disintegrate, thereby causing gas leaks to appear at the pipe joints.
The decay of joint filler due to the conversion to low-moisture gas is not unique to the United States. The United Kingdom is experiencing similar decay of their gas pipe joint filler. As a preventative measure, and as an attempt to slow down the decay of filler material, many gas companies in the United Kingdom, and a few in the United States, routinely xe2x80x9cfogxe2x80x9d their gas lines. Fogging normally involves sending a glycol type product through the gas pipeline to enhance the moisture content of the filler. Another method of maintaining high moisture in the filler involves a process known in the gas industry as humidification. This process requires repeated application of pressurized steam to a gas pipe system.
Unfortunately, these preventative procedures are only temporary and can be quite costly. Today, to adequately prevent gas from escaping these types of pipelines, the pipe joints or other discontinuities must be sealed or replaced. Because many of these pipelines are underground and not readily accessible, excavating, removing and replacing an entire length of pipeline having deteriorated pipe joints is drastic and quite costly.
One method of sealing these pipe joints or other discontinuities against gas leaks is to excavate each joint or discontinuity individually and apply an exterior seal or patch to the pipe at the point of the leak. This method, however, is time consuming, expensive and requires an extensive amount of natural resources to fill and patch each excavation. Another method of sealing gas pipe joints or other discontinuities against gas leaks includes excavating an end of the pipe and having someone climb into the pipe to hand apply a coating compound. This method can also be quite expensive and time consuming. Also, this method can be dangerous and is unfeasible for small diameter pipe. Another technique includes inserting a permanent lining throughout the entire length of pipe. Again this is quite costly and may cause an unacceptable reduction in the flow capacity of the pipe. Also, this method requires a large consumption of natural resources to fabricate a lining for an entire length of pipe, when typically only the joints are susceptible to leaking.
Still another method, such as U.S. Pat. No. 4,178,875 (1979, Moschetti) includes sending a device through the pipe that can remotely detect a joint or other discontinuity that needs repair. A coating material is then sent through attached tubing and is sprayed onto the inner surface of the pipe at the desired location. However, this and the above-mentioned methods are not performed on xe2x80x9clive gas pipexe2x80x9d(pipe in which pressurized gas remains flowing). These methods require the gas flow to be shut down for long periods of time. Depending on the customers being serviced by the gas line, it is normally unacceptable to interrupt service for such long periods of time. Another disadvantage of these methods is that they require more than a single excavation when coating long lengths of pipeline.
Still other methods are known whereby the gas remains live while coating, repairing or sealing is accomplished. U.S. Pat. Nos. 4,582,551 and 4,627,471 (1986, Parkes et al.) disclose a method and device that can remotely seal joints or leaks in a pipe while the gas continues flowing in the pipe. The device is inserted into a pipe whose inner diameter is slightly larger than the outer circumference of the device. The device uses expandable bladders to form a substantially air-free environment, thereby isolating the joint or discontinuity from pressurized gas. The pressurized gas is rerouted through the interior of the device. Anaerobic sealant is then pumped to the device and the sealant is sprayed onto the interior of the pipe at the desired location. The device remains in place long enough to allow the anaerobic sealant to setup. A disadvantage with this device is that it requires an environment free from air and flowing pressurized gas in which to apply sealant. Another disadvantage with these types of devices is that they are limited in their ability to maneuver around corners or other obstacles in the pipeline as they are in close proximity to the interior of the pipe. Still another disadvantage with these devices is that they are slow and time consuming because they require the device to remain in place while the sealant sets.
Another method of sealing pipe joints in a live gas pipe is taught in U.S. Pat. No. 5,156,886 (1992, Kitson). This method involves inserting a nozzle attached to a hose through a tapping mandrel to a desired location in a live gas pipe, whereby an anaerobic sealant is pumped through the hose to the nozzle. The nozzle sprays the anaerobic sealant onto the interior of the pipe. This method works well on relatively short lengths of pipe. However, as the length of tubing increases, the viscosity of the anaerobic sealant prevents it from reaching the spraying device in adequate quantities. Also, as the length of tubing increases, static electric charges build up in the line due to the friction caused by the sealant rubbing against the interior of the tubing. This can pose serious problems when working in a live gas setting. Another drawback with this device is that the anaerobic sealant tends to pool in the bottom of the pipe upon application. An additional drawback of this method is that it typically requires the presence of some filler to properly seal a leaking joint. Because the above-mentioned preventative or fogging measures were never routinely performed in the United States, much of the filler in United States gas pipe joints has disintegrated, making this method of sealing pipe joints impractical.
What is needed is an apparatus and method for inserting a coating device into live gas pipe. What is also needed is an apparatus and method of propelling a coating device through long lengths of live gas pipe. What is further needed is an apparatus and method that can remotely control a coating device while inside a live gas pipe, is safe to use in live gas settings and that requires only a single excavation.
It is therefor an object of the present invention to provide an apparatus and method for inserting a coating device into the passageway of a live gas pipeline.
It is another object of the present invention to provide an apparatus and method for laterally propelling a coating device through the passageway of long lengths of live gas pipeline.
It is still a further object of the present invention that it be safely operable in live gas settings.
It is still a further object of the present invention that it requires only a single excavation to repair several hundred feet of live underground pipe.
These objects are achieved by providing an apparatus and method for safely inserting a coating device into the passageway of a live gas pipeline and precisely propelling the coating device laterally through long lengths of the live gas pipeline passageway.
As thousands of miles of these types of pipe deteriorate all over the United States and the rest of the World, and because the present invention allows several hundred feet of underground pipe to be coated or repaired using a single excavation, the required number of excavations needed to repair the deteriorating pipe and pipe joints will be greatly reduced. Therefore, the energy and natural resources required to restore the excavated repair sites will also be greatly reduced. In addition, the present invention will provide an economically feasible method of repair that allows indefinite postponement of the replacement of thousands of miles of gas pipeline, thereby preserving the enormous quantities of natural resources that would be required to fabricate replacement pipe. As many of these pipe joints and other discontinuities are sealed, the loss of natural or propane gas will be greatly reduced, as will the consumption of enormous amounts of glycol and other joint filler preserving compounds.